lib/atomic64_test.c: add a test that atomic64_inc_not_zero() returns an int
authorMichael Ellerman <mpe@ellerman.id.au>
Fri, 14 Jul 2017 21:49:41 +0000 (14:49 -0700)
committerLinus Torvalds <torvalds@linux-foundation.org>
Fri, 14 Jul 2017 22:05:13 +0000 (15:05 -0700)
commitffba19ccae8d98beb0a17345a0b1ee9e415b23b8
tree296a447d459113fb7fb12c25c238409c542b9485
parent37511fb5c91db93d8bd6e3f52f86e5a7ff7cfcdf
lib/atomic64_test.c: add a test that atomic64_inc_not_zero() returns an int

atomic64_inc_not_zero() returns a "truth value" which in C is
traditionally an int.  That means callers are likely to expect the
result will fit in an int.

If an implementation returns a "true" value which does not fit in an
int, then there's a possibility that callers will truncate it when they
store it in an int.

In fact this happened in practice, see commit 966d2b04e070
("percpu-refcount: fix reference leak during percpu-atomic transition").

So add a test that the result fits in an int, even when the input
doesn't.  This catches the case where an implementation just passes the
non-zero input value out as the result.

Link: http://lkml.kernel.org/r/1499775133-1231-1-git-send-email-mpe@ellerman.id.au
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Cc: Douglas Miller <dougmill@linux.vnet.ibm.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
lib/atomic64_test.c